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Antarctic Plumbing Teleconference Multimedia Resources

02.15.07

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Presenter #1 - Helen Amanda Fricker, Associate Research Geophysicst at the University of California

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Image above: Title slide shows photographs taken in the field in the late 1980's of collapse structures observed on Whillans Ice Stream during an airborne survey. It is thought that these features are associated with subglacial water movement similar in nature to that described in this briefing. Image credit: Charlie Bentley and Lee Powell, University of Wisconsin.

Image above: Title slide shows photographs taken in the field in the late 1980's of collapse structures observed on Whillans Ice Stream during an airborne survey. It is thought that these features are associated with subglacial water movement similar in nature to that described in this briefing. Image credit: Charlie Bentley and Lee Powell, University of Wisconsin.

Image above: Schematic illustrating how ICESat works and how it makes precise, repeat surface height measurements which were critical to the findings reported in this briefing. Image credit: NASA ICESat project.

Image above: Left : MODIS Mosaic of Antarctica (MOA) of the lower Whillans and Mercer ice streams with total range (i.e. highest minus lowest) in ICESat height measured over the period 2003-2006 with ICESat. Places with high range values represent areas that changed the most. The maximum range value was 9m or 30 ft (about the height of a 3-story building), and this occured in two regions. Our interpretation is that the elevation changes are the surface expression of subglacial water moving beneath the ice streams. Regions that are rising in height are filling with water and those that are falling are draining. Image credit (MOA): Ted Scambos and NSIDC ICESat data credit: NASA and Helen Amanda Fricker. Right: ICESat repeat height profiles for two track segments where the elevation range was high. Image credit: Helen Amanda Fricker Data credit: NASA ICESat project.

Image above: This slide shows a zoom in to the first lake we discovered -- this lake showed up as a large thining signal in the ICESat repeat track data near the grounding zone of Ross Ice Shelf. This is a subglacial flooding event which occurred over 2.75 years. In the paper, we refer to the 300 km^2 lake as Subglacial Lake Engelhardt for the ridge that it lies next to. ICESat height changes along 7 ground tracks are drawn on top. This slide also shows detailed height profiles both across and along the lake. Image credit (MOA): Ted Scambos and NSIDC, ICESat data credit: NASA and Helen Amanda Fricker.

Caption for animation above: The following animation helps to explain the dynamics of subglacial water exchange and how we can see it from space. Starting from an actual satellite image of the study area, we dissolve into an artists concept of the Antarctic surface. The camera then moves down to a cross section of the ice sheet with lakes hidden deep beneath. As pressure is exerted on one lake, the water in it is forced to an adjacent lake. This water movement results in elevation changes at the surface over both lakes, detectable by NASA satellites. The camera then moves to a “top-down” view of a system of these hidden lakes and streams before dissolving into actual observed satellite data. Credit: NASA

Image above: Title slide shows photographs taken in the field in the late 1980's of collapse structures observed on Whillans Ice Stream during an airborne survey. It is thought that these features are associated with subglacial water movement similar in nature to that described in this briefing. Image credit: Charlie Bentley and Lee Powell, University of Wisconsin.

Image above: The ICESat signals were confirmed for two of the lakes by a new technique called satellite image differencing. This technique is sensitive to changes in surface slopes on the ice, and this is the first time the technique has been applied to find changes on the ice streams. Image differencing confirmed the drainage event that we saw in the ICESat data over Lake Engelhardt, and also over Lake Mercer. Image credit: Ted Scambos and NSIDC.

Image above: Left : Same as for slide #5. Right: This image shows the estimated hydrologic potential pressure under the ice, i.e. the pressure exerted at the base of the ice. It is derived from the surface elevation and the bedrock topography, but it is the surface elevation that dominates (by about a factor of 10). We expect that water will pool where the hydro-potential is low, and be pushed away from places where it is high. When we plot the events on top, we find that their locations indeed closely coincide with potential lows. This map suggests there are three distinct regions in the hydro-potential, and lakes within those regions should be linked. There is some evidence of this linkage in the ICESat height data. Image credit: Ted Scambos, NSIDC. Data credit: NASA and Helen Amanda Fricker.

Image above: This is a three dimensional rendition of the hydro-potential. The four main lakes are marked. Image credit: Ted Scambos, NSIDC.

Image above: Title slide shows photographs taken in the field in the late 1980's of collapse structures observed on Whillans Ice Stream during an airborne survey. It is thought that these features are associated with subglacial water movement similar in nature to that described in this briefing. Image credit: Charlie Bentley and Lee Powell, University of Wisconsin.

Image above: Change in elevation against time at three ICESat crossovers (points where two tracks intersect) in the centre of Subglacial Lake Engelhardt, which illustrates the drainage pattern for this lake. The inferred drainage path for the floodwater to the ocean is indicated by a yellow arrow. The total amount of water lost to the ocean over 2.75 years was 2.0 km ^3 (2 x 10^11 litres). This is enough water for everyone in the USA to have 5 US gallons (20 litres) of water per day for one year. Image credit: Ted Scambos, Helen Amanda Fricker.

Image above: This slide summarizes the amount of water contained in the system over the study period. Excluding Lake Engelhardt, the remainder of the system had a net water gain of 0.6 km^3 per year for this period. Image credit: Ted Scambos, Helen Amanda Fricker.

Image above: Title slide shows photographs taken in the field in the late 1980's of collapse structures observed on Whillans Ice Stream during an airborne survey. It is thought that these features are associated with subglacial water movement similar in nature to that described in this briefing. Image credit: Charlie Bentley and Lee Powell, University of Wisconsin.